Android: Fix race/crash when switching away/back to the emulation activity

android/app/src/cpp/android_host_interface.cpp

@@ -447,6 +447,11 @@ void AndroidHostInterface::SurfaceChanged(ANativeWindow* surface, int format, in
     wi.surface_height = height;
 
     m_display->ChangeRenderWindow(wi);
+
+    if (surface && System::GetState() == System::State::Paused)
+      System::SetState(System::State::Running);
+    else if (!surface && System::IsRunning())
+      System::SetState(System::State::Paused);
   }
 }
 
@@ -523,7 +528,8 @@ void AndroidHostInterface::SetControllerAxisState(u32 index, s32 button_code, fl
     false);
 }
 
-void AndroidHostInterface::RefreshGameList(bool invalidate_cache, bool invalidate_database, ProgressCallback* progress_callback)
+void AndroidHostInterface::RefreshGameList(bool invalidate_cache, bool invalidate_database,
+                                           ProgressCallback* progress_callback)
 {
   m_game_list->SetSearchDirectoriesFromSettings(m_settings_interface);
   m_game_list->Refresh(invalidate_cache, invalidate_database, progress_callback);

android/app/src/main/java/com/github/stenzek/duckstation/EmulationActivity.java

@@ -29,7 +29,6 @@ public class EmulationActivity extends AppCompatActivity implements SurfaceHolde
     private SharedPreferences mPreferences;
     private boolean mWasDestroyed = false;
     private boolean mStopRequested = false;
-    private boolean mWasPausedOnSurfaceLoss = false;
     private boolean mApplySettingsOnSurfaceRestored = false;
     private String mGameTitle = null;
     private EmulationSurfaceView mContentView;
@@ -128,10 +127,6 @@ public class EmulationActivity extends AppCompatActivity implements SurfaceHolde
             AndroidHostInterface.getInstance().surfaceChanged(holder.getSurface(), format, width, height);
             updateOrientation();
 
-            if (holder.getSurface() != null && !hadSurface && AndroidHostInterface.getInstance().isEmulationThreadPaused() && !mWasPausedOnSurfaceLoss) {
-                AndroidHostInterface.getInstance().pauseEmulationThread(false);
-            }
-
             if (mApplySettingsOnSurfaceRestored) {
                 AndroidHostInterface.getInstance().applySettings();
                 mApplySettingsOnSurfaceRestored = false;
@@ -159,8 +154,6 @@ public class EmulationActivity extends AppCompatActivity implements SurfaceHolde
         if (!mStopRequested)
             AndroidHostInterface.getInstance().saveResumeState(true);
 
-        mWasPausedOnSurfaceLoss = AndroidHostInterface.getInstance().isEmulationThreadPaused();
-        AndroidHostInterface.getInstance().pauseEmulationThread(true);
         AndroidHostInterface.getInstance().surfaceChanged(null, 0, 0, 0);
     }
 

src/frontend-common/opengl_host_display.cpp

@@ -124,6 +124,9 @@ bool OpenGLHostDisplay::DownloadTexture(const void* texture_handle, u32 x, u32 y
 
 void OpenGLHostDisplay::SetVSync(bool enabled)
 {
+  if (m_gl_context->GetWindowInfo().type == WindowInfo::Type::Surfaceless)
+    return;
+
   // Window framebuffer has to be bound to call SetSwapInterval.
   GLint current_fbo = 0;
   glGetIntegerv(GL_DRAW_FRAMEBUFFER_BINDING, &current_fbo);

src/frontend-common/vulkan_host_display.cpp

@@ -234,6 +234,9 @@ bool VulkanHostDisplay::DownloadTexture(const void* texture_handle, u32 x, u32 y
 
 void VulkanHostDisplay::SetVSync(bool enabled)
 {
+  if (!m_swap_chain)
+    return;
+
   // This swap chain should not be used by the current buffer, thus safe to destroy.
   g_vulkan_context->WaitForGPUIdle();
   m_swap_chain->SetVSync(enabled);